Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $233.35   5.834%   $246.9636   $246.96   $246.95   $247.00  
  Purchase #2 $244.58   10.793%   $270.9775   $270.98   $271.00   $271.00  
  Purchase #3 $174.92   8.508%   $189.8022   $189.80   $189.80   $189.80  
  Purchase #4 $81.46   10.356%   $89.896   $89.90   $89.90   $89.90  
  Purchase #5 $223.93   12.783%   $252.555   $252.56   $252.55   $252.60  
  Purchase #6 $193.55   8.776%   $210.5359   $210.54   $210.55   $210.50  
  Purchase #7 $205.98   4.160%   $214.5488   $214.55   $214.55   $214.50  
  7 purchase totals = $1,357.77       $1,475.2790   $1,475.29   $1,475.30   $1,475.30